The present invention relates to bushings in general and more particularly to helically wound bushings.
In U.S. Pat. Nos. 4,003,562 and 4,043,567, both assigned to the same assignee as the present application, there are disclosed spiral bushings, for use, for example, in heavy motor vehicle spring shackles and steering knuckle assemblies. The spiral bushings disclosed therein are made from flat strips of high grade tool steel cut at an angle at each end, bevelled and notched on the edges. The strips are helically wound into a cylindrical configuration resembling a helical tension spring in that each coil or spiral abuts the adjacent coil or spiral. The tapered ends of the strips provide square ends when the strips are wound into a cylindrical configuration. The strips are rectangular in cross-section with a ratio of width to thickness of about 7 to 1.
The helically wound cylinder is, after annealing, placed in a die, and sized for roundness by hydraulically driving a sizing mandrel through them. The bushings are subsequently heat treated for hardness, ground, and honed in their interior. Their peripheral surface is ground, after which a contra-helical grease distribution groove is formground on the peripheral surface to prevent blockage of the grease port if improperly oriented during installation, the bevelled edges of the strip providing external and internal lubricant distribution grooves, and the edge notches lubricant passageways from the external grooves to the internal grooves.
The resulting product is a precision tool steel helically wound bushing or bearing having the unique capability of being manually installed in and removed from a bore by twisting axially thus reducing the outside diameter of the bushing sufficiently to eliminate the interference fit with the bore. Once installed in the bore, the bushing springs back to a compression fit. However, such bushings are high in material cost, processing costs, and other associated production costs.